1. Field of the Invention
The present invention relates to a thermal layer, a backlight unit and a display device including the same. Particularly, the present invention relates to a thermal layer capable of improving the temperature character of a display device, as well as a backlight unit and a display device including the same.
2. Description of the Related Art
A Liquid Crystal Display device hereinafter, referred to as a “LCD device”) is an electrical device which changes electrical data generated from many apparatuses into visual data, and transfers them by using variation of liquid crystal transmissivity according to applied voltage.
A LCD device is a device for displaying information, but does not have a light source in itself. Thus, a LCD device needs an extra device to uniformly brighten the entire screen by a light source installed at the rear surface of the LCD device. As such an extra device, a Back Light Unit (hereinafter, referred to as a “BLU”) is used to provide light to the screen of the LCD device.
A BLU is classified into either a direct-light type or an edge-light type according to the installed position of a light source. In a direct-light type of BLU, the light source is disposed under the liquid crystal panel, and in an edge-light type of BLU, the light source is disposed on the side of light guiding plate.
An edge-light type of BLU comprises a light source unit, a light guiding plate, a reflector, and an optical film.
The light source unit comprises at least one light source generating light with a predetermined wavelength, and a light source reflector. The light generated from the light source is reflected by the light source reflector, which is made up of reflective material, and the reflector. Then, the reflected light is diffused uniformly through the entire light guiding plate.
The optical film comprises a diffuser, a prism sheet, and a protection sheet.
The function of each element in the optical film is explained as follows.
The light uniformly diffused in the light guiding plate passes through the diffuser. The diffuser diffuses or condenses the light having passed through the light guiding plate so that the brightness is uniform and the viewing angle is wider.
However, the brightness of the light after having passed through the diffuser is remarkably decreased. To solve this problem, a prism sheet is used. The prism sheet refracts the light having passed through the diffuser, and converges the light incident in low angle to the direction substantially perpendicular to the prism sheet so that the brightness is increased within the range of the effective viewing angle.
The protection sheet is disposed on the prism sheet. Thus, the protection sheet prevents the prism sheet from being damaged, and widens the narrowed viewing angle.
A Cold Cathode Fluorescent Lamp (hereinafter, referred to as a “CCFL”) is used mainly as the light source of the BLU. As the LCD device emits light by the BLU installed to a liquid crystal panel, the inside temperature of the LCD device increases, and the temperature of the CCFL increases up to 80° C. to 90° C.
Thus, the efficiency of the BLU lowers, and the brightness of the LCD device decreases.
Unlike an edge-light type of BLU, a direct-light type of BLU has a reflector under the light source. In this structure, most heat generated from the light source is transferred to the reflector. The reflector is overheated by the transferred heat, and thus may be deformed.
Also, though it may be different according to the type of BLU, most heat generated from the CCFL is transferred to the liquid crystal panel disposed on the front surface of the BLU, and thus a temperature difference between liquid crystal cells may occur. Such temperature difference between liquid crystal cells causes a difference in response velocity between liquid crystal cells, and thus becomes a cause of brightness difference of the LCD device.
A Plasma Display Panel (hereinafter, referred to as a “PDP”) is a light-emitting display device having a structure wherein a plurality of discharge cells are disposed between a pair of glass substrates, and need not have an extra light source unlike a LCD device. But, it is a well-known fact that in a PDP, a discharge cell that is induced to emit light for displaying an image generates heat, whereby the temperature of the PDP increases. That is, the heat generated in the discharge cell is transferred to the glass substrate, but is not transferred in a direction parallel to the panel surface due to the characteristic of glass materials having low thermal conductivity.
Also, the temperature of the discharge cell activated for emitting a light is remarkably increased, but the temperature of the discharge cell not activated is not increased that much. Thus, the temperature of the panel is increased partly in an image-forming area. This temperature difference may induce heat declining of the discharge cell affected thereby.
Besides the LCD device or the PDP described above, such heat problems occur in display devices using an emitting diode or organic electroluminescent devices, and is a factor deteriorating the durability or the display quality of the device.
Thus, there has been a need to develop a way to effectively radiate heat generated in such devices to the outside.